Fault indicator for radio relaying systems



Feb. 1, 1949. L E. THOMPSON FAULT INDICATOR FOR RADIO RELAYING SYSTEMS original m04 rgb. s, 1945 5 Sheets-Sheet 1 ATTORNEY Feb. 1, 1949. l.. E. THoMPsoN y FAULTv INDICATOR FOR RADIO RELAYING SYSTEMS.

Original Filed Feb. 6, 19745 5 Sheets-Sheet 2 Feb. l, 1949. E. 'rH'oMPsoN FAULT mnrcnon Foa mmm RELAYING sYsTl-:us

Original. Filed Feb. 6, 1945 5 Sheets-Sheet 3 Feb. 1, 1949. L. E. n-mlvyPsolxl 2,460,789

FAULT INDICATOR FOR RADIO RELAYING SYSTEMS mlf @05 AMP. L/M..

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v vvvvuvv" "vv wwwww u l si 63V any AINVEN TOR. y iM/V0 5. THe/wsa# y ATTORNEY Feb. l, 1949. L. E. THoMPsoN FAULT INDICATOR FOR RADIO RELATING SYSTEMS y Drignal Filed Feb. 6, 1945 5 Sheets-Sheet 5 Patented Feb. 1, 194D Leland E. Thompson, Merchantvill'e, N. J., al-

signor to Radio Corporatio poration of Delaware nofAmei-icmacor- Original application February 0, 190B. Serial No.

Divided and this application March l5, 1940, Serial No. 054,551

My present invention which is a division of my copending application. Serial No. 576.453. illed February 6, 1945. deals with radio relaying.

Radio relaying is useful for many purposes. For example, radio relays may be used to convey a program originating in a studio to a distant broadcast transmitter. The relay oiiers advantages over wire lines for that purpose since the wire lines are expensive to construct and have serious limitations with respect 'to frequency band widths which they are capable of transmitting. In general, unless carefully designed, costly wire lines are built, there may be serious loss in the quality and fidelity of the signals or programs carried by the lines. Radio relaying offers similar advantages over cables and wire lines, when simplex or multiplex signals are to be transmitted across rivers, bays and other bodies of water and over mountains. deserts and other difficult terrain.

When relaying with very short waves having frequencies of the order of. for example, 3000 megacycles per second the distance of transmission is limited principallyby the curvature of the earth since the short radio waves tend to act like light `waves and travel in straight lines without useful refraction or reflection from the Heaviside layer as is the case with longer waves. This necessitates the use of relays spaced about twenty or thirty miles apart depending upon such things as the height of the supporting structure available for the transmitting and receiving antennas. For a trans-continental radio relay employing ultra short waves it may be necessary. therefore, to use over one hundred relaying stations.

My present invention is particularly directed to and has for an object, the provision of improved apparatus for indicating failure or breakdown in any station of an extensive relay system.

In the accompanying drawings, f

Figure l illustrates schematically a transmitting terminal for an ultra high frequency relay system. The terminal makes use of a high quality voice channel having, as indicated, an upper frequency of 10.000 cycles although if desired. this may be raised to 15,000 cycles and several other signaling channels which are transmitted to a common amplifier as side bands of suitable sub-carriers. All of the signals are combined. pre-emphasized in a suitable network and used to frequency modulate a common sub-carrier having, as illustrated, a mean frequency of one megacycle. The latter, in turn. is used to freterminal.

11 Claims. (CL 177-411) quency modulate a transmitted carrier having a mean frequency of 3,000 megacyclcs. l/

Figure 2 is a block diagram of a typical relay station employing the principles of my present invention.

Figure 3 is a block diagram oi a receiving This terminal may receive waves transmitted directly from the apparatus of Figare to be read as joined along the line XX so inclusive.

lthat the conductors A to -L inclusive are respectively connected together. Figure 4 is illustrative of apparatus which, in accordance with my present invention, indicates break own at any relay station in the relaying Systei.

In Figure 1. several independ nt signaling channels are combined and modulate the waves radiated from the transmitting antenna TA to the receiving antenna RA200 of the relay\ station of Figure 2. The waves received at"` the relay station are heterodyned. amplified detected and used to modulate a different carrier frequency wave. The latter is radiated over the relay transmitting antenna TA2|4 to the receiving antenna RA000 of Figure 3. The received waves at thel receiving terminal are amplified, translated and separated into signalscorresponding to those originally transmitted.

Turning more specifically to Figure 1. the signal channels are designated by the letters A to 1l',

T'hese channels are combined in resistor 23 and fed through transformer 24' and pre-emphasizing network VPN to oppositely frequency modulate oscillators 20 and |02.

Oscillator 2l may operate. by way of example.

at an unmodulated frequency of 10 megacycles and oscillator |02, for example, at an unmodulated frequency of l1 megacycles. The outputs of the two oscillators 20 and |02 are combined in the converter |00 as a result of which the frequency modulation appearing in the peak frequency output of converter |00 is equal to the sum of the deviations of the oscillators 2l and |02 when they are caused to separate in frequency.

It will, therefore, be apparent that each oscillator, in the arrangement of Figure 1, need swing only half as farl as would be the case if only one oscillator were used to produce a given amount of frequency modulation. As a consequence, distortion is reduced since the working range of the oscillators is made smaller and over the smaller range they can be made more. linear in action. Cross-modulation between channels is therefore greatly reduced` Furthermore, such an serves to reduce ;hu m due to illamentfheating o'r ripple in the plate voltage supply- A The frequency modulated output of the com verter Il( is a beat of one megacycle plus and minus 170 kilocycles and is us'edto frequency modulate a second frequency modulated oscillator |04 whose mean unmodulated frequency' is 3000 megacycles.

' -As a result'the wave radiated over the transmitting antenna TA of Figure l is a 3000 megacycle carrier having a maximum deviation of plus and minus 1.0 megacycle. Agreater deviation ratio for the waves modulated in frequency modulator may be used if desired so that the transmitted wave would be of the order of 3000 'mega'- cycles plus and minus two `or four megacycles.

More specifically, with reference to the channels A to?, inclusive, channel A is a high quality voice channel containing all frequencies in the band from 30 to 10,000 cycles.

The high quality voice signal is picked up by microphone 2, amplified by amplifier 4 and sent through lter B'and another amplifier 8 to the combining resistor 28.

Channels B to F, inclusive, are low quality voice channels each passing through the first amplifiers 4B, 4C, 4D, 4E and 4F, different voice signals lying in the band from 30 to 4,000 cycles.

These amplified signals are fed to the modulators I2B to I2F, inclusive, supplied with oscillations from separate oscillators 0B to IiiF, inclusive. The output of the modulator |2B is fed through a filter MB which passes' only the lower side band. Similarly, filters |4C to IdF, inclusive, pass only the lower ade bands produced, respectively, ln modulators I2C to I2F, inclusive. In the case of filterv MB the'ha'nd of frequencies passed on to ampliner IBB occupies the range from l2 to 16 kilocycles.

Similarly, the lower side band lters IHC to MF, inclusive, pass on to ampliers IBC to IBF.

n. inclusive. the lower side bands derived from the immediately preceding modulators I2C to 12F inclusive. The frequency band passed by each side band filter is indicated in Figure 1. Thus |00 passes 20-24, kilocycles, etc.

. The f'outputs f the lower side band amplifiers I 0B to IGF inclusive are combined as indicated and fed through a band pass filter to amplifier 4 frequency modulate the second frequency modulated oscillator l operating at an unmodulated carrier frequency' of 3000 megacycles.-

Thedeviation ratio of the modulated waves appearing in the output circuit of the second frequency modulated oscillator |04 is unity or more, as desired, as a result of which the waves radiated over the transmitting antenna TA have for maximum deviation a frequency of 3000 megacycles 10 fully modulated.

The waves radiated from the transmitting antenna TA of'Figure 1 may be received directly by the receiving apparatus of Figure 3. Ordinarily, however, such waves would be radiated to the receiving terminal by way of one or more 22, which is made as linear as possible to prevent cross-modulation between channels. Ihe output of ampliiler 22 is combined with the output of the high quality channel from amplifier 8 inv resistor 'I'he resulting voltage across resistor 23 occupies aband of frequencies from 30 to 48,000 cycles and this band is fed through transformer 2s to the oppositeiy frequency modulated oscillators 25'an' s |02 having, respectively, unmodulated carrier 'frequencies of ten and eleven megacycles. Adjustments are made, as explained in my'parent application as, that when all of the channels are fully modulated and when they are all additive vof the converter |00 of Figure l.

relaying points, such as illustrated in Figure 2. The waves would be received at the relay point in the system at some different frequency so as to avoid feed-back or singing at the relay station.

In the relaying system illustrated in Figure 2, the waves are picked up or received on a receiving antenna RA200. The received waves are beat down in frequency in a converter circuit 202 with waves from a local beating oscillator 204. The intermediate frequency produced may be 30 megacycles plus and minus 1.0 megacycle. The waves of intermediateV frequency are amplified in an intermediate frequency amplifier 200 and then fed to a discriminator detector 208.

The action of the discriminator detector is such as to produce a wave of one megacycle plus and minus kilocycles corresponding to the' output This wave is limited and amplified in appropriate apparatus 2|0 and then used to frequency modulate oscillator 2I2 whose unmodulated frequency may be 3010 megacycles.

By adjusting the amplitude of the output of amplifier 2I0 the waves radiated over the transmitting antenna TA2 I4 of the relay point of Figure 2 may be made 3010 megacycles plus and minus 1.0 megacycle.

The waves radiated from the transmitting antenna TA2I4 of the relay point of Figure 2 are received on the receiving antenna RA300 of the UHF. relay system receiving terminal illustrated in Figure 3. These Waves are heterodyned with waves from a local beating oscillator 304 in a converter 302 to produce an intermediate frequency of thirty megacycles plus and minus 1.0 megacycles. -These 'waves of intermediate frequency are amplied in the intermediate frequency amplifier 306 and then fed to a first discriminator detectorV 308. As before explained, a high degree of ampliication is secured with amplifier 305.

The output of the first discriminator detector 308 is the one megacycle plus and minus 170 kiloycle wave corresponding to the output of the converter |00 of Figure 1. The output of the first discriminator detector 308 of Figure 3 is then amplified and limited in amplifier` limiter 3|0. Hence, it will be observed that the forward portion of the apparatus of Figure 3 from RA300 to the limiter 3I0 is substantially identical to the apparatus between RA200 and limiter 2 l0 of Figure 2, as a result of which economy in the design and flexibility in the use of the apparatus are 'secured.

anonce megacycles from oscillator 818. The upper beat of converter 3H is fed to discriminator detector 3|2, in the output leads 8I8 of which appear a band of frequencies from and including 30 to 48,000 cycles corresponding to the band of frequencies fed through transformer 24 of Figure 1 to the frequency modulated oscillators and |02.

Of this band of frequencies filterv IBAR, to which the band is fed through amplifiers 84, 88, passes the high quality voice channel A containing waves lying in the band of to 10,000 cycles. These waves are amplified in the amplifier 40AR and fed to a loudspeaker or earphones A. The other frequencies corresponding to the lower side bands of channels B to F inclusive of Figure 1 and occupying the band from 12 to 48 kilocycles are fed through band pass lter 44 and amplifiers 46 to 54 inclusive to the filters 58 to 84 inclusive.

Filters 50 to 84 inclusive pass bands of frequencies as indicated in Figure 3, namely, lfilter 56 passes 12 to 16 kilocycles, filter 58 passes 20 to 24 kilocycles, filter 80 passes 28 to 32 kilocycles, filter 62 passes 36 to 40 kilocycles and filter 64 passes 44 to 48 kilocycles. The outputs of filters 56 to 84 are combined in the converters 88 to 14 with oscillations from local oscillators 81, 88, 1|, 13 and 15 operating, respectively, at 16 kilocycles, 24 kilocycles, 32 kilocycles, 40 kilocycles and l48 kilocycles. Each of the filters 18 to 84 'is designed to pass a band of frequencies from 30 to 4000 cycles, as a result of which in the amplifiers 85 to 94 inclusive the originally transmitted signals B to F inclusive appear. These waves are individually translated as indicated, by the earphones B, C, etc.

Also it is to be noted that all of the channels need not be voice channels, but if desired, some of them may be telegraph channels. some voice and some of the other types, such as facsimile and teletype channels. Thus, as a possible alternative channel A may be replaced by twelve telegraph channels, the separate telegraph carrier tones of which may occupy the band from 465 to 2295 cycles, each tone channel having a width of 170 cycles. Thus, the first telegraph channel may be designed for a tone carrier of 465 cycles with a signaling width of -plus and minus 85 cycles, the second tone channel may use a tone carrier of 595 cycles with a cycle width of plus and minus 85 cycles, etc.

In addition to channels A-F inclusive, of Figure 1, a service channel SC may be provided. The output of the service channel pick-up microphone may be amplified by the service channel amplifier SCA and switched directly, by means of switch SCS, to frequency modulate oscillator |04. Preferably, ampliflerSCA passes a band of approximately 0-5000 cycles and the amplitude of the modulating voltages is adjusted so as to produce, for example, a maximum swing of $15,000 cycles in the output of oscillator |04.

As indicated in Figure 2 the service channel band may be filtered out by filter SCF and taken ure 4 also represents in wiring diagram form the apparatus contained within' rectangles 208. 208 and 810 of Figure 3.

That is. as before explained, the output of the converter 202 of Figure 2 or 802 of Figure 3 is a wave of intermediate frequency, such as 30 megacycles having a deviation of :1.0 megacycle. This intermediate frequency wave, as before explained in connection with Figures 2, 3 and in my parent application, is fed through transformer primary 1|5 (Fig. 4a) to the tuned secondary coil 128 tuned by condenser 128, the lower terminal of the tuned circuit being grounded for high frequency currents by means of a bypass condenser 120. 4

As indicated in Figure 4a, the output of the tuned circuit 128, 128 is fed through leadf'l32 to the amplifying tube 800 which forms part of the first amplifying stage of the intermediate frequency amplifier. The output of tube 800 is fed through properly tuned circuits 802 to the second amplifying tube 804. The output of amplifier 804 is fed through tuned circuits to the amplifiers and Hunters 808 and 8| 0. To insure limiting action in tubes 808 and 8|0, either or both may be operated with reduced plate voltage. The output of limiter 810 is fed into a tuned circuit 8|2 tuned to the mid-intermediate frequency, and for the case described previously, to 30 megacycles. Circuit 8|2 excites the discriminator detector system comprising tuned circuits 8|4, 8|8 and the double diode detector 8|8. Circuits 8I4 and 8|8 are tunedso as to have overlapping resonant characteristics.

The output of the discriminator detector system 8|4, 818 and 8|8, appears across resistors 102, 184 shunted by high frequency lay-passing condensers 820. 822 and fed through tuned circuit 824, broadened by the loading resistor 826, to the control grid of the amplifier 828. Circuit 824 is tuned to have a mean frequency of one megacycle corresponding to the mean frequency of the output of discriminator detector 208 and this corresponds to the mean frequency of the.

output of the converter |00 of Figure 1. Condenser 880 is of such value as to pass the waves of one megacycle plus and minus deviation of kilocycles, but substantially impedes or otherwise blocks the frequencies of the service channel BC of Figure 1. The service channel frequencies are, therefore, fed through conductor 882, resistor 188 and condenser 836 to the audio amplifier 828 in the output of which there is provided a suitable monitoring jack 840. Also, there is provided a patch cord or lead 842 suitably tapped to the plate resistor 843 in case it is desired to modulate the high frequency oscillator 2 I2 at the relaying point with the service channel for transmittal on to the next station whether the latter be another relaying point or terminal receiving station.

The sub-carrier frequency output of amplifier 828 (Figure 4b) is fed through tuned circuit 844, amplifier limiter 845. tuned circuit 846, amplifier limiter 841, tuned circuit 848. by-passlng condenser 848, and transmission line 850to the frequency modulated oscillator 2|2 of Figure 2. It will be appreciated. of course, that circuits 844, 848 and 848 of Figure 4 are tuned to the su'bcarrier frequency'resulting from the first discriminator detector action of 814, 8|8 at the relaying or receiving points. Accordingly. if used at a relaying point, such as shown at Figure 2, these circuits would be tuned to one megacycle and designed so as to be broad enough to pass a bando! frequencies of :170 kilocycles.

It is to benoted that a portion of the output of the discriminator detector arrangement 8M, 8|6.

' 8|8-of Figure 4 is used to automatically frequency control the first beating oscillator 204 of Figure 2 or 304 of Figure 3 to maintain the beat frequency output of the converter 202 of Figure 2 or 302 of Figure 3 within the by-pass band of the intermediate frequency amplier 206 of Figure 2 or 308 of Figure 3. That is to say, a part of the output of detector 8I8 of Figure 4 is fed through 1ead'832, resistor 186 and resistor 190 tothe grid iM-of tube 160. Resistor 190 and condenser 192, the latter connected between grid 164 and ground, are chosen so as to have a time constant sufiiciently fast to substantially remove the quick parent application.

Should the intermediate frequency of one megacyclein the arrangement of Figure 4 fail for any reason, it will be noted that the D. C. voltage built up across resistor 880 in the grid circuit of limiter tube 865 by the normal signal will also fail. Hence, the negative voltage in conductor 86| will drop to approximately zero. As a consequence,

the normal negative bias on the grid 862 of tube' 863 will drop to approximately zero and this tube will conduct .plate current through plate 864, lead 865,*resistor 866, conductor 861, and relay coil 868. thereby .effectively grounding point 869. In othei words, point 869 will be brought effectively to the potential of cathode 810 of tube 863.

. Asa result, `oscillator 81| previously blocked by application of positive potential, derived from point p69. to its grid 812 will go into oscillation and produce oscillations of a frequency determined by the tuning of its grid circuit 813 which is preferably tuned to some frequency in the intermediate frequency pass band, such as, for example, 1.1 megacycles. A part of the output of oscillator 81| is fed through lead 814 to a point 815 in tuned circuit 824.

Thevoltage built up across circuit i826 by waves from the local oscillator 81| is adjusted so as to be of much lower amplitude than the norm'al intermediate frequency .signals passing' through the system, as a result of which, the di- Should lthe signal intermediate frequency of one megacycle fail, then it will be found that the noise level will tend to rise abruptly. The presence of the injected wave from such oscillator 81| of Figure 4 will curtail and otherwise suppress this rise in noise voltage.

Also, in order to indicate failure of the intermediate !requency signal, the. relay. 888 may be 8 used to close a contact 810A completing a circuit from a source of potential 819 to an "alarm bell 880 and an indicating light 88|. If desired, contact 810A may be used to operate a coding device in turn used to key a tone `which may be fed into the service channel or be .permanently connected to the service channel so as to give a further indication, according to the particular code and tone frequency employed, of the point at which break-down occurred.

What is claimed is:

1. In combination, a, high frequency amplifier comprising a tube having anode, cathode and grid electrodes, a source of waves to be amplified connected to said grid and cathode, a resistor connected between a pair of said electrodes for developing a direct current control potential in the presence of signal waves to be amplified, a high frequency oscillator, circuits utilizing said direct current potential to prevent said oscillator from oscillating and for permitting said oscillator `to oscillate in the absence of said control potential, and a circuit for feeding a potential from said oscillator to the input of said amplifier when said control potential fails.

2.' Apparatus asV claimed in the preceding claim, characterized by the fact that said oscillator is connected to a point of relatively low impedance in the input circuit of said amplier.

3. In combination, an amplifier having an anode, a cathode and a grid, a circuit including a. coil connected between said cathode and grid for subjecting/the input electrodes of said amplier to alternating waves to be amplified, a resistor connected between said grid and cathode, said resistor having direct current control potentials developed thereacross in the presence of signal waves to be amplified, an oscillation generator adapted to generate waves of a frequency lying in the range of' frequencies amplified by said amplier, a circuit connected from said resistor to apply said control potentials to said generatorin such a way as to prevent oscillation generation thereby when said lcontrol potential is developed, and a connection from said oscillation generator to a point of low impedance on said coil, said connection serving to feed waves from said generator into the input circuit of said amplier when said control potential drops to a value such as to allow said oscillation generator to generate oscillations.

4. In combination, an amplifier having an ties connecting said resistance to said indicating device, said instrumentalities including a vacuum tube, ior causing operation of said indicating device in the absence of direct current flow through said resistance.

5. In combination, a rst amplier tube having an anode, a cathode and a grid, an input circuit including a coil connected between said cathode and grid for subjecting the input electrodes of said amplifier to alternating waves to be amplified, a second amplifier tube, a. resistor connected between saidgrid and cathode of said second ampliiler tube, said resistor having direct current control potentials developed thereacross in the presence of signal waves to be amplied, an oscillation generator adapted to gen'- erate waves of a frequency lying in the range of' frequencies amplified by said amplifier, a circuit circuit of said amplier tubewhen said control potential drops to a value such as to allow said oscillation generator to generate oscillations.

6. In electrical apparatus, a vacuum tube operating 'as a limiter, said tube having anode, cath.- ode and grid electrodes, a circuit for applying waves to be limited across the grid and cathode of said limiter, an output circuit connected to the anode and cathode of said limiter, a resistor connected between two of the electrodes of said limiter tube whereby a voltage is developed across said limiter in the presence of predetermined input Waves across the grid and cathode of the limiter, an oscillation generator the operation of which is to be controlled and circuits responsive to the voltage drop across 1said resistor to control the operation of said oscillation generator and means for utilizing oscillations generated by said generator to convey infomation as to the failure of application of said waves to the quency modulated; and by the fact that theresistor is connected between the grid'and cathode of said limiter tube.

9. In electrical apparatus, a vacuum tube lim,

. 10 f iter having an anode, input circuit connected between the grid and cathode, an output circuit connected between the anode and cathode, means for feeding waves in said input'circuit, said waves being repeated in said Voutput circuit, a resistor connected between two of the electrodes of said tube, the connection being such that a control voltage is developed across said resistor in the presence of input waves of-predetermined amplitude, an oscillation generator, the output of which is to be controlled, a control tube having an anode, a cathode and aI grid, a circuit for feeding the voltage drop across said resistor to thergrid and cathode of said control tube and instrumentalities for utilizing the anode-cathode circuit of said control tube to control the output of said generator and means for utilizing oscillations generated 4by said generator to convey information as to the failure of application of said wavesin said input circuit to said limiter. Y

10. Apparatus as claimed in claim 9 characterized by the fact that said vacuum tube operates as a limiter; by the fact that frequency modulated waves are fed to 'the input side thereof for repetition in the output circuit thereof and by the fact that a circuit is provided for feeding waves from said oscillation generator to the input side of said limiter.

11. Apparatus as claimed in claim 10 characterized by the fact that said resistor is connected between the grid and cathode of the limiter.

I LELAND E. THOMPSON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED l STATES PATENTS Number Name Date 2,296,384 Hansell Sept. 22, 1942 2,315,434 Leibe L Mar. 30, 1943 2,315,435 Leibe Mar. 30, 1943 a. cathode and a grid, an v 

